This invention relates to optical apparatus for tracking a path of movement of a tool along a line of travel on a workpiece, and in particular, to a compact apparatus which allows the tool to be operated in confined areas. This invention also relates to a filter for use with a seam welding system having a torch which generates spark trails.
Optical apparatus for tracking a path of movement of a tool along a line of travel on a workpiece have been developed which employ a projected light stripe to track the path of movement based on the geometry of the light stripe. An optical system (e.g., a camera) is used to collect data relating to the geometry of the light stripe, and three-dimensional information is calculated to describe, for example, part type, location and orientation. This information is then ultimately used to alter the path or control the operation of a tool, such as an industrial manipulator or a hard automation device. An example of one such light stripe tracking system is described in U.S. patent application Ser. No. 756,002, filed July 17, 1985, now U.S. Pat. No. 4,652,133, by R. S. Antoszewski et al. and assigned to the assignee of the subject application, the contents of which are hereby incorporated by reference. This application describes a light stripe seam tracking system which is employed on a seam tracker for a welding apparatus employing a torch. This type of seam welding apparatus is manufactured and sold by Westinghouse Electric Corporation. The optical tracking apparatus employs a light stripe generating apparatus and an imaging apparatus for generating an image of the light stripe on the workpiece. The optical assembly, including both the light stripe generating apparatus and the imaging apparatus, is placed in an enclosure in front of the torch along the line of travel of the torch. In addition, a relatively bulky helium neon laser is employed as a light source. As a result, the optical assembly enclosure protrudes approximately 4 inches in front of the seam welder, thereby making it difficult to employ the seam welder in confined areas (e.g., when it is necessary to continue a weld to a position abutting a wall or a bulkhead).
Several attempts have been made to reduce the size of the optical assembly for seam trackers. In one apparatus, a fiber optic bundle is placed in front of the torch and the light stripe is centered along the line of travel using a termination block, a lens and an aperture. In another apparatus, a cylindrical mirror is placed in front of the torch to create the light stripe, and additional mirrors and lenses are employed to properly position the light stripe along the line of travel. Despite the above attempts to decrease the size of the optical assembly, it has not been possible to make the optical tracking apparatus sufficiently compact because the optical assembly has been positioned in front of the seam welder along the line of travel. Thus, there remains a need in the art for a compact optical tracking apparatus which is capable of accurately tracking a path of movement of a tool even when the tool must be used in confined areas (e.g., abutting a wall or a bulkhead).
Light stripe tracking systems of the type described in U.S. Pat. No. 4,652,133 also typically employ a camera which is pointed downward to focus on the light stripe projected on the workpiece, and which is positioned adjacent the torch. As a result, it is necessary to provide a spatter shield in front of the camera so as to protect the camera from spattering and film build-up on the camera. Even if a spatter shield is employed, it is necessary to replace the spatter shield often due to film build-up on the shield itself. Further, even if a spatter shield is employed, there remains some distortion in the image generated by the camera. This distortion is a result of the glare generated by the torch and the spark trails in the image which are generated as a result of welding. With respect to spark trail distortion, television images of welding processes, and especially metal inert gas (MIG) processes, suffer from visual interference caused by sparks and spatter passing through the field of view of the camera. Since area-type television cameras are inherently integrating devices, the sparks and spatter produce intense streaks in each video frame. In seam tracking systems, these streaks can easily be confused with the image of the light stripe projected onto the workpiece and can lead to an error in the calculated three-dimensional position measurement. Thus, there is a need to remove the streaks from the image without modifying the light stripe signal itself. In summary, there is a need in the art for an optical apparatus which is capable of providing a clear image of a projected light stripe without the presence of distortion caused by glare or spark trails.